High capacity fiber transmission already provides the technical means to move very large amounts of data from node to node at reasonable cost. Broadband access systems are based on systems such as fiber to the home, fiber to the curb, coaxial cable, or wireless, and will serve to connect subscribers to local access nodes. As the number of asynchronous transfer mode (ATM) broadband subscribers grows, and total network traffic volume increases, the construction of an efficient access and tandem network will require very large ATM switches with aggregate capacities in the 100's to 1000's of gigabits per second (Gbit/s).
Innovations in network architecture may lead to a more distributed network of a larger number of smaller nodes, but the geographic clustering of traffic in cities and communities, the shrinking cost of collecting a large bandwidth over ring, tree, or star access networks, and the operational economics of fewer, larger sites is likely to continue to favor the concentration of traffic into exchanges serving 10,000 to 100,000 subscribers. Similarly, fewer but larger tandem switches will be more economical. Local and tandem exchanges capable of switching 5,000 to 80,000 Erlang of voice traffic are already common today. Extending from this existing telephone network capacity and assuming that traffic patterns and communities of interest do not change substantially, a simple estimate of switch sizes would be 0.4 to 5 Gbit/s at 64 kbit/s.
Traffic demand and average bit rates of terminals in the broadband network are less predictable. Average peak hour demand may range from a few 100 kbit/s to 10 Mbit/s or more per subscriber, depending upon the offered service. For example, digital video-on-demand, using MPEG2, could easily generate a network demand of 5 or 10 Mbit/s per household (the bottleneck in this scenario appears to be the video server capacity).
It would require a gross switching capacity of one Terabit/s to handle the aggregate demand of a 100,000 subscriber head end switch. Similarly, millions of already existing home computers could transfer data over a broadband network at peak rates well in excess of 10 Mbit/s, if such a network were offered economically.
Today, ATM switches which address both the data and the evolving multi-media market are being offered. These switches have capacities ranging from less than 600 Mbit/s to a few 10's of Gbit/s. The task of switching much larger amounts of point to multi-point or point-to-point traffic efficiently will have to be solved in future.
In U.S. Pat. No. 5,126,999, issued Jun. 30, 1992 (Munter et al), an ATM switch is described in which output segregated input buffers are operated on real-time by crosspoint selection circuits implementing a combined buffer fill/age algorithm.
In U.S. Pat. No. 5,241,536, issued Aug. 31, 1993 (Grimble et al), a timeslot utilization means is provided in an ATM switch for scheduling the earliest possible connection between an input port and output ports.
In U.S. Pat. No. 5,130,975, issued Jul. 14, 1992 (Akata), a timeslot scheduling unit in an ATM switch prevents the packets from collision in a space division switching unit. Each packet buffer unit at each port writes packets sequentially but reads out randomly in the timeslots assigned by the timeslot scheduling unit so that the throughput of the space division switching unit is improved.
In U.S. Pat. No. 5,157,654, issued Oct. 20, 1992 (Cisneros), a contention resolution technique for a large ATM switch is described. It utilizes cell address look-ahead in conjunction with parallel planes of self-routing cross-points, staggered time phased contention resolution and shared memory based input and output modules.
In U.S. Pat. No. 4,956,839, issued Sep. 11, 1990 (Torii et al), an ATM switch includes ATM line terminating units and a self-routing space switch.
The overall architecture of the switches of the present invention is based loosely on a space switch crosspoint, input and output buffers and substantially high speed links connecting them. None of the above patents is concerned with packet switches in which a train of one or more ATM cells are transmitted by way of high speed links through a space crosspoint in one burst.